Planets at a 90-degree angle from each other are said to be Square. Imagine a hurdle in a track meet. You are motivated to get over the hurdle, but it takes extra planning and effort. A Square ties two or more planets together in such a way that they are challenged to work together. This challenge often manifests as tension and stress.
However, people who learn how to work with the difficult aspects of their chart often accomplish more that those who have charts filled with easy aspects.
Signs that are square to each other: